The invention relates to polyolefin blends which have superior physical properties including enhanced toughness at high reinforcement levels for high performance use in molded articles such as automotive vehicle bumpers or the like. The invention also relates to molded articles as well as to methods for producing them.
In numerous applications, such as many in the automotive industry, a polymeric material that exhibits a good balance of toughness and rigidity is desired. These properties tend to occur inversely however, and efforts to enhance one will often result in deterioration in the other. Special polymeric materials have been developed that overcome this problem to some degree.
European Patent Application 0794225-A1 discloses thermoplastic resin compositions comprising polypropylene, a styrene containing elastomer and talc wherein an acceptable balance of toughness and rigidity is reported. The disclosure stresses the importance of the proportions of each component used to achieve this balance.
In PCT Application WO97/38050, a similar balance of properties is reported for a thermoplastic resin comprising an ethylene-propylene based polymer composition, an ethylene-alpha olefin copolymer based rubber and/or a rubber containing vinyl aromatic compounds and talc. Another example of a composition with an acceptable balance of toughness and rigidity is reported in Japanese Patent Application 10-219040-A for a resin composition consisting of a polyolefin based resin and a block copolymer based on aromatic vinyl and butadiene monomer units.
A comparative study of mechanical properties of compositions like those disclosed in the foregoing references is reported in Kiyoo Kato et al. New Developments in Styrenic Block Copolymers (SEBS) for Polypropylene Modification, Fifth International Conference, xe2x80x9cTPO""s in Automotive ""98xe2x80x9d, Oct. 12-14, 1998, Novi, Mich. There is confirmation therein that a good balance of toughness and rigidity is exhibited by such compositions. Kato and his colleagues also report results from a related morphological study in this same paper, and it can be concluded from these results that the styrene based components in these compositions promote toughness at least by segregating at the interface of the other components and entangling with polymer chains in the various phases.
Despite these prior art formulations, there remains a need to obtain other polymeric materials with a good balance of toughness and rigidity, and the present materials satisfy this need.
The present invention relates to polyolefin blends comprising a base component of a propylene containing polymer, a portion of which is functionalized with a hydrophilic moiety; a toughening component of polymer selected from the group consisting of (A) a copolymer of ethylene and an alpha olefin and (B) a terpolymer of ethylene, an alpha olefin and a diene; an interfacial modifier in the form of an elastomeric block copolymer; and a filler. In these blends, the functionalized polypropylene is present in an amount sufficient to ensure dispersion of the filler with the semicrystalline portion of the blend. This permits a higher weight fraction of the filler within the polypropylene phase, leading to superior reinforcement. The toughening agent is present in an amount sufficient to enhance low temperature impact properties of the blend, the interfacial modifier is present in an amount sufficient to assist in adhesion between the polymer components of the blend, and the filler is present in an amount sufficient to enhance blend strength and hardness.
Another aspect of the present invention is a method for making an article of manufacture comprising the step of molding the described polyolefin blend into a desired configuration and shape of the article of manufacture. The resultant molded articles and their use as automotive components are further aspects of the invention.